The present invention relates to a printing mechanism such as a carriage assembly and in particular to a carriage assembly for a typewriter or any other type of impact printer wherein the spacing between the printing element on the carriage assembly and the platen must be adjusted.
Prior art printing units which are of the impact type require periodic adjustment of the space between the platen which holds the paper and the printing element itself. This is accomplished in the prior art by mounting the cylindrical platen in the printer frame such that the cylindrical platen can be adjusted in both the vertical and horizontal planes. This requires, of course, at least two overlapping plates on the printer frame in which the platen is mounted and in which the platen may be adjusted by moving one of the plates in the horizontal or vertical plane and then after it is properly adjusted in that plane that plate is locked so that no further movement can take place in that plane and then the second plate is adjusted which allows movement of the platen in the second of the two planes until the proper spacing adjustment is obtained and then that plate is locked. As can be expected, such mechanism is rather complex and, in addition, is difficult to adjust in one plane without affecting the adjustment in the other plane. Great care must be taken so that this interference does not occur.
The present invention overcomes the disadvantages of the prior art by allowing the platen to be adjusted in only the vertical plane and thus the relative horizontal position of the printing mechanism and the platen with respect to each other is adjusted by moving the printing mechanism with respect to the platen in a horizontal plane. In the present case, the printing mechanism is mounted on a pulley support assembly which, in turn, is mounted on a cylindrical support or shaft which is attached to the printer frame parallel to the axis of the platen whereby if the cylindrical support or shaft is moved in a horizontal plane towards or away from said cylindrical platen, the horizontal space between the printing mechanism carried by the pulley support assembly and the cylindrical platen is adjusted. Therefore, horizontal adjustment of the support or shaft which carries the pulley support assembly and the carriage assembly with the printing mechanism thereon has no effect on the physical position of the cylindrical platen and there is no interaction between the two other than the space therebetween being adjusted. In like manner, if the cylindrical platen is adjusted in the vertical plane, it has no interaction with the adjustment of the support member on which the printing mechanism is being carried by the pulley support assembly. Therefore, the problems of the prior art are obviated by the present invention in a manner which is simple and yet effective.